In recent years, a liquid crystal display element is used in various fields, and in particular, is largely used in a field of electronic industries such as a notebook personal computer, portable liquid crystal television, and the like, since the liquid crystal display element is thin-type and lightweight. This liquid crystal display element indicates image by controlling light transmission/shielding from an external light or back lighting (internal light source) by means of a liquid crystal shutter, since the liquid crystal display element does not emit light in itself unlike a plasma display. Namely, in a liquid crystal display element, a diffusing film, which is to provide a light in uniformly to an entire liquid crystal panel, is inserted into the backside of a liquid crystal panel in general. A reflective film that has high diffused reflectance is used in the liquid crystal display which uses an external light. The reflective film scatters and reflects the external light which is entered from the obverse side of the liquid crystal panel and returns to the liquid crystal panel. The display indicates image by controlling transmission/shielding by means of a liquid crystal shutter. While a diffusing film that has high diffused transmittance is used in the liquid crystal display which uses a back lighting. The diffusing film diffuses and transmits the internal light from the reverse side of a liquid crystal panel and provides a light to the liquid crystal panel. Transmission/shielding of light is controlled by means of the liquid crystal shutter. Further, a semitransmissive diffusing film which properly uses the external light and the back lighting according to ON/OFF of the back lighting, also can be used.
Conventionally, as for a technique regarding a transmissive diffusing film which diffuses a light flux from a back lighting, the technique mentioned in Japanese Unexamined Patent Publication No. Sho 57-88401 is known. Also, as for a technique for complementing a color tone, the technique mentioned in Japanese Unexamined Patent Publication No. Sho 60- 250382 is known.
A transmissive diffusing film mentioned in said Japanese Unexamined Patent Publication No. Sho 57-88401 comprises one pearly pigment and diffuses a light flux from a back lighting by this pearly pigment.
On the other hand, in addition to said pearly pigment, a polarizer disclosed in said Japanese Unexamined Patent Publication No. Sho 60-250382 further comprises fluorescent dye, blue dye and the like. A color tone is obtained by absorbing an optical component which has a specific wavelength among a light flux from the back lighting, to dye.
However, the light transmittance in the case where white light was entered, was low in short wave range as compared with long wave range, in the diffusing film mentioned in said Japanese Unexamined Patent Publication No. Sho 57-88401, as shown in FIG. 1a. Therefore, a color tone of a transmitted light in a diffusing film became dark liver brown and satisfactory color tone and lightness could not be obtained even when this diffusing film was used for a liquid crystal display element.
Also, a polarizing film mentioned in said Japanese Unexamined Patent Publication No. Sho 60-250382 is exemplified as for a technique to complement an inferiority of color tone. However, an incident light from a back lighting was not effectively used since an optical component which has a specific wavelength among the incident light from the back lighting was absorbed by dye. Accordingly, satisfactory color tone and brightness could not be obtained even in the case where these dyes were used in the diffusing film. Also, in view of the stability of color tone, satisfactory diffusing film were not obtained because dyes were easily deteriorated by light.
A semitransmissive liquid crystal display element which uses an external light or an internal light according to well-lighted time or darkened time, spent lower power than a transmissive liquid crystal display element which continuously uses a light flux from an internal light source.
A semitransmissive liquid crystal display element needs to have light transmittance that a semitransmissive diffusing film which was located between a liquid crystal panel and an internal light source, uniformly diffuses a light flux from the internal light source when the internal light source was switched ON and light reflectance that the semitransmissive diffusing film uniformly diffuses the light flux entered from an external portion to the liquid crystal display element and reflects again to an external direction when the internal light source was switched OFF.
As for a technique to obtain a transmitted light and a reflected light by white light in the case where white light is entered to a semitransmissive diffusing film, the technique mentioned in Japanese Unexamined Patent Publication No. Hei 8-179125 is exemplified.
A semitransmissive diffusing film mentioned in said Japanese Unexamined Patent Publication No. Hei 8-179125 uses one white pearly pigment in a substrate. Namely, white transmitted and reflected light in the semitransmissive diffusing film are obtained by whitening the pearly pigment in itself.
However, in the case where white light was entered to the semitransmissive diffusing film mentioned in said Japanese Unexamined Patent Publication No. Hei 8-179125, for example, the transmitted light became dark liver brown, since light transmittance in the semitransmissive diffusing film was low, as like the transmissive diffusing film, in short wave range as compared with long wave range as shown in FIG. 1. Therefore, satisfactory color tone and brightness could not be obtained.
Accordingly, though this semitransmissive diffusing film was used in a lighting unit or semitransmissive liquid crystal display element, satisfactory color tone and brightness were not obtained nevertheless.
Further, the more labor-saving power is required in the case where a liquid crystal display element is used as portable type or on-vehicle type liquid crystal display element. In particular, downsizing and lightening of a portable apparatus becomes necessary with rapid spread of portable use such as a portable telephone, a personal digital assistants (PDA), and the like. Therefore, a reflective liquid crystal display element which uses an external light without using a lighting unit (back lighting unit) which occupies a large part of electricity consumption, is expected.
A conventional reflective liquid crystal display element was a black-white display. A metal deposited film, a polishing metal plate, and the like which has metallic luster were used as a reflective film. Also, a semitransmissive diffusing film mentioned in Japanese Unexamined Patent Publication No. Hei 8-179125 which has the same reflectivity as a reflective film in spite of a semitransmissive diffusing film, was exemplified.
However, said conventional reflective film which has metallic luster sometimes caused a so-called greasiness that luminance was extremely decreased excluding a specular reflection angle, though said reflective film had high specular reflection luminance. In the case where this reflective film was used in a liquid crystal display element, visibility was sometimes spoiled.
Also, a semitransmissive diffusing film disclosed in said Japanese Unexamined Patent Publication No. Hei 8-179125 uses one white pearly pigment in a substrate. Namely, white reflected light in the semitransmissive diffusing film was obtained by whitening the pearly pigment in itself.
However, when white light was entered to a reflective film in the case where one of this white pearly pigment was used in a reflective film, there was a fear that the light reflectance at the reflective film became low in long wave range in comparison with in short wave range. Accordingly, satisfactory color tone and brightness were not obtained even when these reflective films were used in the reflective liquid crystal display element.